Locating the position and direction of a target item regardless of the surroundings has long held promise as particularly desirable. Thwarting child abductions, for example, is greatly simplified if the location and direction of travel of a child is available at all times to a parent. Additionally, monitoring the direction and location of an expensive asset, such as a laptop computer, allows misplaced items to be quickly found while simultaneously preventing theft. Knowing the last location and direction of travel of an item assists searchers, as their initial search may be directed along probable pathways as opposed to searches that start in a large geographic area without any preliminary guidance. Since the probability of locating an item diminishes greatly with the passing of time between the actual abduction or theft and the realization that the tracked item is missing, limiting the search area assists in rapid recovery.
While this position and direction information is desirable, its implementation into a suitable product has proved difficult. Traditionally, there have been two classes of tracking apparatus; those that rely on direct radio communication and those that use a satellite system such as a GPS. The radio communication systems are typically burdened by size restrictions and are limited to ranges which support direct radio frequency communication. In the event a monitor or target strays into an area where RF communication between the monitor and target cannot be maintained, tracking is interrupted and the target is lost. For example, if a child in a large indoor mall strays beyond the range of a parent monitor, this results in the loss of all tracking information. This child may now continue to stray further from a parent, in any direction, without the parent receiving updated position and direction information. As the distance increases, and the child's haphazard directions continue to change, locating this child becomes substantially more difficult.
The satellite tracking systems are also limited by their ability to receive external position signals. Some modern tracking systems use global positioning data (GPS) to pinpoint the location of an item. For example, a vehicle may have an on-board GPS receiver coupled to a RF transceiver for broadcasting the location of the vehicle following the report by the owner that the vehicle has been stolen. A thief may have stolen the vehicle several hours before the tracking report was initiated, and driven the vehicle a long distance from the scene of the crime. During this time, the position and location of the vehicle are unknown unless there was a constant monitoring system. This is inefficient in energy and not practical. If the vehicle is concealed in a setting that does not allow for the reception of a GPS signal, such as in a garage or under heavy tree cover, locating the vehicle using the on-board tracking system is no longer possible. Additionally, existing GPS based tracking systems are typically large in physical size, and have substantial power demands. While such physical size and power requirements are normally not of concern when the tracking device is located within the confines of a motor vehicle, it may be for other uses.
Many existing tracking only address position tracking in a two dimensional environment (i.e., along the X and Y axes). In the aforementioned shopping mall environment, a child may moved between floors (i.e., in the Z axis direction) while still remaining within RF communication with a mobile parent monitor. In such a scenario, the child appears in close physical proximity on a parent monitor display, but is in actually well beyond the “safe zone” of the parent. If the parent monitor indicated the child has strayed beyond the predefined safe zone, a parent attempting to locate this child is faced with the dilemma of locating a child that may be several floors above or below his current position. In such a setting, a child abductor can cover a great distance before the last know position of the child is determined.